Michael R. Olofson, 50, of Antioch.

A registered sex offender from Antioch was arrested after police say he sexually assaulted two young girls, who were between ages 4 and 12, over the span of a year more than a decade ago.

The Lake County Sheriff’s Office said a report was filed in December regarding a sex offense and detectives began an investigation.

They determined several acts of sexual assault occurred more than 10 years ago at a residence in the 39400 block of North Highview Drive in unincorporated Antioch.

The suspect who committed the assaults was identified as Michael R. Olofson, 50, of the 39400 block of North Highview Drive in unincorporated Antioch, who is a registered sexual offender.

The victims were related to Olofson and he committed numerous acts of sexual assault on the girls over the duration of more than a year, according to Lake County Sheriff Spokesman Lt. Christopher Covelli.

Olofson is a convicted sex offender due to a previous conviction for possessing child pornography.

Following a thorough investigation conducted by sheriff’s detectives, they arrested Olofson at his residence on Saturday, Covelli said.

Sheriff’s detectives reviewed the facts and circumstances of the case with the Lake County State’s Attorney’s Office.

Prosecutors approved two counts of predatory criminal sexual assault of a child, a Class X felony, and three counts of aggravated criminal sexual abuse, a Class 2 felony.

“As with all victims of abuse, the victims in this case had a lot of courage to come forward and discuss the abuse they endured for years. I want every victim of sexual assault to know we are always here for you. We will always be your advocate and will always do everything we can for you,” Sheriff John D. Idleburg said.

Olofson remains held in the Lake County jail on a $100,000 bond. He is scheduled to appear in court on February 23.